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UBC Theses and Dissertations

Design and characterization of an actuator test fixture for diesel fuel injectors Hossain, Syed Tanjid


The High-Pressure Direct Injection of Natural Gas in a diesel engine is one of the innovative solutions to reduce diesel engine pollutants. The quantity and quality of the fuel injected is highly depended on the spray pattern, which controls the air and NG fuel mixture in the combustion cylinder. Fuel release is regulated by a needle, that is linked to a solenoid actuator through a hydraulic system. An actuator with position feedback can control the spray pattern of a fuel injector by controlling the needle displacement of the injector. However, the relationship between the actuator displacement and injector needle displacement is unknown. Therefore, an Actuator Test Fixture (ATF) is designed that simulates the injection process of a typical hydraulically actuated fuel injector. It allows the researcher to study and ultimately model the relationship between actuator displacement and needle motion. In contrary to conventional fuel injectors, the ATF provides measurement access to all model parameters and allows their characterization. Thus, a characterized model is created that describes the relationship between the actuator displacement and ATF needle motion. The model of the ATF combines both the mechanical aspect of the components and the hydraulic mechanics of the fuel. There are two inputs to this model, the experimentally measured actuator displacement and experimentally measured supply pressure. ATF needle lift and control chamber pressures are the outputs of the model. The experimental-model comparison showed good agreement. The model is verified across several different operating points by varying the supply pressure and the actuator pulse duration to increase confidence in the experimental-model results. At high supply pressure, the model fits very well but as the pressure reduces the model starts to show discrepancy. This is likely due to un-modeled friction effects in the ATF. Nevertheless, the experimental-model control chamber pressures and needle lifts are very similar.

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